Federal railroad experts investigating this week's Blue Line crash said Wednesday their early findings have led them to consider emergency recommendations to the CTA, a move that would signal concerns of a future accident.

Investigators didn't elaborate on those findings or what any recommendations could entail, but that consideration came even as the CTA reopened the Harlem station, where the accident occurred, and normal service along the Blue Line resumed Wednesday.

The four rail cars and the eight-car Blue Line train it hit were towed, one car at a time, Tuesday night to a CTA facility for examination and testing, officials said.

Officials from the National Transportation Safety Board, which is leading the inquiry into Monday's accident involving an apparently empty and out-of-service train, were collecting what they called "perishable evidence" at the crash site Wednesday and expect to finish on-scene work by Saturday. The agency's overall investigation is expected to take a year and result in a report on the crash's probable cause.

NTSB investigators began testing the electronic and mechanical systems on the four rail cars for anomalies that would help explain how the parked cars, which are more than 30 years old, were suddenly set in motion and traveled a half-mile during Monday morning's rush period, an investigator said.

After it left the Forest Park yard, the out-of-service 2600 Series train somehow made it through two track interlockings without being stopped by metal "trip" strips that stick up out of the ground. When tripped by a train that is going against the intended direction set by CTA personnel in a control tower, the strips are supposed to activate a lever on the side of the rail cars that throws the train into an emergency stop.

The "ghost train," as some CTA rail employees dubbed it, also avoided other "fail-safe'' protections. It reached an estimated speed of 20 mph before slamming into an in-service train that was stopped at the Harlem station, CTA officials said. A preliminary review of security video has revealed no sign of anybody onboard the rogue train, CTA officials and Forest Park police said.

The NTSB officials investigating the CTA crash continued their work even as the federal government shutdown paused other agency efforts, in large part because of the sensitivity of the evidence and because of the possibility of imminent safety threats, said Sharon Bryson, the NTSB's deputy communications director.

More than 30 riders on the in-service train suffered minor injuries, and the first lawsuit stemming from the accident was filed against the CTA on Wednesday in Cook County Circuit Court. The suit alleges that the CTA "carelessly and negligently" operated the trains in the collision.

"This accident calls out to the citizens of Chicago and the visitors to our city who rely upon the CTA to provide a safe transit to their destinations," attorney Robert Smoler said on behalf of his client, Kim Quach, who was identified as a passenger on the train that was struck.

The CTA's 2600 Series rail cars operating on the Blue Line were built between 1981 and 1987 by the Budd Co. of Philadelphia.

Two of the four cars that escaped from the rail yard Monday had been on hold since late September, waiting to be taken to the CTA's Skokie Shop repair facility, CTA officials said.

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